"There is no optimistic scenario"

(Adds U.N. estimate of regional aid needs)

By Nellie Peyton

DAKAR, March 29 (Thomson Reuters Foundation) - Food shortages and a jihadist uprising in northern Burkina Faso risk plunging the region into a humanitarian crisis if urgent action is not taken, aid agencies said on Thursday.

Much of West Africa's Sahel, a semi-arid belt below the Sahara, is facing its worst hunger in years after erratic rains caused little vegetation to grow.

Nearly a million people in Burkina Faso are expected to need food aid in the coming months, with one in ten already suffering acute malnutrition in the north, government statistics show.

But escalating violence will make it difficult for aid agencies to help in the remote area about 250 kilometres (155 miles) north of capital Ouagadougou, the Red Cross and the United Nations said.

"There is no optimistic scenario," Christian Munezero, head of mission for the International Committee of the Red Cross (ICRC), told the Thomson Reuters Foundation.

Attacks by Ansarul Islam, a militant group founded by a radical preacher in 2016, are becoming increasingly frequent and deadly, the International Crisis Group said this month.

More than 18,000 people have fled their homes since September and countless clinics have closed, said Munezero.

Dozens of schools, frequently targeted, have also shut, said the United Nations children's agency (UNICEF).

"I think this population has a pretty strong capacity for resilience, which would have allowed them in one way or another to cope with the climate shock, if there weren't this additional factor of insecurity," said Munezero.

Normally the Sahel experiences a hungry season between July and the October harvest, but this year it has already started or is imminent in most places, said World Food Programme (WFP) regional director Abdou Dieng.

"The longer we wait, the more the situation will deteriorate," he said by phone from Ouagadougou.

"If we don't act now, it may get complicated."

Up to 6.8 million people across the Sahel could need food aid by August, the United Nations said this week, a 60 percent increase from the number estimated late last year.

WFP will start giving out food and cash next month in Burkina Faso, on a larger scale than in recent years, Dieng said.

Neighbouring Mali is also facing food shortages and jihadist attacks, but has been for years.

"What is distinctive about Burkina Faso is that this is a new situation for everyone," said Munezero of the ICRC. (Reporting by Nellie Peyton. Editing by Katy Migiro. Please credit Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, women's rights, trafficking, property rights, and climate change. Visit www.trust.org)